The present invention relates to a fluid pressure boosting device, which boosts operating force exerted on an operating means with working fluid pressure, controlled by a control valve, into predetermined magnitude to output the boosted force and a brake system employing the fluid pressure boosting device. More particularly, the present invention relates to a fluid pressure boosting device which can set the input stroke into various values without being affected by the operation of a working unit of a master cylinder and the like operated with the output of the fluid pressure boosting device and can control the output of the fluid pressure boosting device during its operation regardless of the operating force exerted on the operating means and a brake system employing the fluid pressure boosting device.
For example, in a conventional brake system of an automobile, a brake fluid pressure boosting device has been employed which intensifies pedal pressure on a brake pedal by fluid pressure of hydraulic fluid into predetermined magnitude to develop large brake fluid pressures. The brake fluid pressure boosting device functions to obtain large braking force from small pedal pressure on the brake pedal, thereby securing the braking action and reducing the fatigue of a driver.
In the conventional brake fluid pressure boosting device, a control valve is actuated by an input based on the pedal pressure on the brake pedal to develop working fluid pressure of hydraulic fluid and the developed working fluid pressure is introduced into a power chamber, thereby intensifying the input at a predetermined ratio to output intensified pressure. A piston of a master cylinder is moved by the output of the brake fluid pressure boosting device so that the master cylinder outputs master cylinder pressure. The master cylinder pressure is introduced as braking pressure of hydraulic fluid into wheel cylinders, thus carrying out the braking action.
By the way, conventional brake systems employ various brake controls such as for controlling the braking force during the braking operation, for example, Anti-Lock Control (ABS), Brake Assist Control to be typically used for starting or stopping in the middle of a slope, and Regenerative Brake Coordination Control to be performed for controlling the braking pressure produced by a service braking system when a regenerative brake system is used to develop braking pressure during the braking operation by the service brake system, and automatic brake controls, for example, a brake control for controlling the distance from another vehicle, a brake control for avoiding a collision with an obstacle object, and Traction Control (TRC).
Most of such brake controls are normally conducted in a brake circuit between the master cylinder and the wheel cylinders. However, when the brake control is conducted in the brake circuit after the master cylinder, it is required to prevent the input stroke of the hydraulic boosting from being affected by such brake controls, for instance, for obtaining better operational feeling.
However, in a brake system in which a conventional brake fluid pressure boosting device and a brake master cylinder are combined, the stroke of a piston of the master cylinder is fixed by the relation between the master cylinder and wheel cylinders so that the stroke of an input shaft of the brake fluid pressure boosting device, i.e. the pedal stroke of a brake pedal, depends on the stroke of the piston of the master cylinder. That is, the stroke for input is affected by the brake controls conducted in the brake circuit after the master cylinder. In the combination between the conventional brake fluid pressure boosting device and the brake master cylinder, the aforementioned requirement can not be securely and sufficiently satisfied.
For changing the stroke characteristic of the brake pedal as the input side to obtain better operational feeling, the brake master cylinder and the brake circuit after the brake master cylinder are also affected so that some change on the output side, for instance a size change on the master cylinder, should be required. By the change on the output side, the output characteristic of the brake system is affected. This means that the overall change on the brake system is required, i.e. large-scale change is required.
It is further desired that the input side is affected as little as possible by brake circuit which may differ according to the type or size of vehicle.
If the input side and the output side are just separated from each other to produce outputs regardless of the travel of the input side, the input side does not travel so that the stroke of the input side can not be ensured.
For this, it has been conventionally proposed that a stroke simulator is provided on the brake circuit after the master cylinder to prevent the travel of the input side from being affected by the brake control after the master cylinder and to ensure the stroke of the input side.
However, to add specially the stroke simulator, many parts such as a stroke cylinder and an electromagnetic switching valve used for the stroke simulator are required, making the structure complex and increasing the cost.
There is still a problem that brakes must be securely operated in case of a fluid pressure source failure even when a stroke simulator is provided.
In an anti-lock control system, it is desired that when a braked wheel or braked wheels are in locking tendency, the braking force is controlled to cancel the locking tendency of the wheel(s). Further, in a regenerative coordination brake system composed of a combination of a service brake system and a regenerative brake system, when the regenerative brake system is operated during the operation of the brake fluid pressure boosting device, the braking force produced by the brake fluid pressure boosting device should be reduced for the braking force produced by the regenerative brake system. In this case, it is desired to reduce the output of the brake fluid pressure boosting device to a value obtained by subtracting the output of the regenerative brake system from the output of the fluid pressure boosting device. In a brake system composed of a combination of a service brake system and a brake assist system, it is desired to facilitate starting at a slope by controlling the cancellation of braking operation and also desired to increase the output of the brake fluid pressure boosting device to intensify the braking force produced by the brake fluid pressure boosting device in such case that brake assist operation is needed, for example, a case that a driver can not depress a brake pedal enough during the operation of the brake fluid pressure boosting device so as not to develop predetermined braking force.
As mentioned above, when the brake control is performed during the operation, the brake pedal is not affected even when the stroke simulator is provided.
Further, in a brake system for controlling the distance from a front vehicle, it is desired to hold the distance constant by automatically actuating brakes when the distance becomes short during running. In a brake system for avoiding a collision, it is desired to avoid a collision with an obstacle object by automatically actuating brakes when there is a possibility of collision with the obstacle object. Furthermore, in a traction control system, it is desired to cancel a slipping tendency to ensure the secure starting by automatically braking driving wheels when the driving wheel(s) is in slipping tendency at the starting.
As mentioned above, it is desired that the brake pedal is not affected when the automatic braking is conducted even when the stroke simulator is provided.
Further, it is desired that such a system for controlling the braking force during braking operation or controlling the automatic braking can be manufactured with a simple structure.
Moreover, it is desired that the input-stroke characteristic, the input-brake pressure characteristic, or the stroke-brake pressure characteristic is allowed to be changed according to the condition of a vehicle or the like with a simple structure.
It is an object of the present invention to provide a fluid pressure boosting device of which the stroke characteristic at the input side can be freely changed without being affected by the output side and without significant modification.
It is another object of the present invention to provide a fluid pressure boosting device which can securely operate even in case of the fluid pressure source failure and which can be manufactured to be compact at a low cost.
It is still another object of the present invention to provide a fluid pressure boosting device of which the output can be controlled regardless of the input of an input member during operation, and to provide a brake system employing the fluid pressure boosting device of which the output can be controlled in response to a request signal requesting an increase or decrease in the output regardless of the input of the input member during operation.
To achieve the aforementioned objects, a fluid pressure boosting device of the present invention comprises at least an input member which is moved by input applied during operation and a control valve which is operated by the input member for controlling fluid pressure of a fluid pressure source according to the travel of said input member to develop working fluid pressure for operating an working unit, and is characterized in that said working fluid pressure acts on said control valve in the inoperative direction, an elastic member is disposed between said control valve and said input member, force of the elastic member corresponding to the travel of said input member acts on said control valve in the operative direction, and said control valve is controlled according to said travel such that the force generated by said working fluid pressure balances with the force generated by said elastic member.
The fluid pressure boosting device of the present invention is further characterized in that in case of said fluid pressure source failure, said working unit is operated by the travel of said input member.
The fluid pressure boosting device of the present invention is further characterized in that said control valve is composed of a spool valve, said spool valve has a valve spool of which operation is controlled by the force of said elastic member acting in the operative direction and by said working fluid pressure acting in the inoperative direction, and the operation of said valve spool is controlled according to the input of said input member in such a manner that force by said working fluid pressure acting on the valve spool balances with force of said elastic member.
The fluid pressure boosting device of the present invention is further characterized in that said spool valve comprises a first throttle valve and a second throttle valve, the flow of hydraulic fluid is first throttled by said first throttle valve and then throttled by said second throttle valve, that is, the flow is throttled at two stages.
The fluid pressure boosting device of the present invention is further characterized in that said control valve is a ball valve or cone valve, the force of said elastic member acts on said ball valve or cone valve in the operative direction and said working fluid pressure acts on said ball valve or cone valve in the inoperative direction, and the operation of said ball valve or cone valve is controlled according to the input of said input member in such a manner that the force generated by said working fluid pressure balances with the force generated by said elastic member.
The fluid pressure boosting device of the present invention is further characterized in that said elastic member is disposed coaxially with said input member, said control valve is disposed to have a predetermined space relative to said input shaft, and further comprising a lever disposed between said elastic member and said control valve wherein said lever being rotated by force of said elastic member corresponding to the travel of said input member to act on said control valve in the operative direction, the position of the pivotal point of said lever is fixed regardless of the travel of said input member, and the operation of said control valve is controlled according to the input of said input member in such a manner that the force generated by said working fluid pressure balances with the force generated by the rotation of said lever.
The fluid pressure boosting device of the present invention is further characterized in that said input member is slidable relative to said lever and a slide lubricating member is provided at a sliding portion between said input member and said lever.
The fluid pressure boosting device of the present invention is further characterized in that said slide lubricating member is a bush or a linear bearing.
The fluid pressure boosting device of the present invention is further characterized in that the pivot point of said lever is positioned on either said input member side or said control valve side.
The fluid pressure boosting device of the present invention is further characterized in that said elastic member is a plurality of springs or a non-linear spring.
The fluid pressure boosting device of the present invention is further characterized in that during the operation when said fluid pressure source is in the normal state, the position of said control valve is fixed regardless of the travel of said input member, and by further comprising a fluid pressure control means for controlling said working fluid pressure regardless of the input of said input member.
The fluid pressure boosting device of the present invention is further characterized by further comprising a power chamber into which the working fluid pressure is introduced to produce an output for actuating said working unit, and a reaction chamber into which said working fluid pressure is introduced to apply reaction force to said input member, wherein said fluid pressure control means is a pressure control valve for controlling the working fluid pressure of at least one of said power chamber and said reaction chamber.
The fluid pressure boosting device of the present invention is further characterized in that said pressure control valve controls said working fluid pressure or the fluid pressure of said fluid pressure source and supplies it into at least one of said power chamber and said reaction chamber.
The fluid pressure boosting device of the present invention is further characterized by further comprising a power chamber into which the working fluid pressure is introduced to produce an output for actuating said working unit, and a pressure control chamber into which said working fluid pressure is introduced to control said output, wherein said fluid pressure control means is a pressure control valve for controlling the working fluid pressure of at least one of said power chamber and said pressure control chamber.
The fluid pressure boosting device of the present invention is further characterized in that said pressure control valve controls said working fluid pressure or the fluid pressure of said fluid pressure source and supplies it into at least one of said power chamber and said pressure control chamber.
The fluid pressure boosting device of the present invention is further characterized in that said fluid pressure control means is an electromagnetic solenoid which generates biasing force biasing said control valve in at least one of an operative direction and an inoperative direction.
The fluid pressure boosting device of the present invention is further characterized in that said control valve comprises a valve spool of which operation is controlled by the force of said elastic member acting in the operative direction and by said working fluid pressure acting in the inoperative direction and a valve sleeve fixed to the housing of said fluid pressure boosting device, and wherein said valve spool is moved relative to said valve sleeve according to the input of said input member in such a manner that force by said working fluid pressure acting on the valve spool balances with force of said elastic member.
The fluid pressure boosting device of the present invention is further characterized in that said valve spool is formed with an annular groove into which said working fluid pressure is introduced during its operation, wherein the pressure receiving area of the pressure receiving surface of said annular groove which receives said working fluid pressure in the inoperative direction of said valve spool is set larger than the pressure receiving area of the pressure receiving surface of said annular groove which receives said working fluid pressure in the operative direction of said valve spool.
The fluid pressure boosting device of the present invention is further characterized by further comprising a lever disposed between said elastic member and said control valve wherein said lever being rotated by force of said elastic member corresponding to the travel of said input member to act on said control valve in the operative direction, the position of the pivotal point of said lever is fixed regardless of the travel of said input member, and the operation of said control valve is controlled according to the input of said input member in such a manner that the force generated by said working fluid pressure balances with the force generated by the rotation of said lever.
A brake system of the present invention comprises a brake fluid pressure boosting device to intensify an input, a master cylinder which is operated with the output of said brake fluid pressure boosting device to develop master cylinder pressure, and brakes which are operated with braking force generated by the master cylinder pressure, wherein said brake fluid pressure boosting device is the aforementioned fluid pressure boosting device, said brake system being characterized in that the operation of said working fluid pressure control means of the brake fluid pressure boosting device is controlled by a controller and that said controller controls the output of said brake fluid pressure boosting device to obtain a requested increase or decrease in the braking force by controlling the operation of said working fluid pressure control means wherein said requested increase or decrease in the braking force is requested by one of other controllers than said controller.
Further, the brake system of the present invention is characterized in that said working fluid pressure control means has an electromagnetic solenoid for its operation, and that said controller for controlling the operation of said working fluid pressure control means supplies electric current to said electromagnetic solenoid wherein said electric current corresponds to the amount of said requested increase or decrease in the braking force requested by said one of the other controllers.
In the fluid pressure boosting device of the present invention structured as described above, the elastic member produces force corresponding to the travel of the input member by the input applied to the input member. The force of the elastic member acts on the control valve in the operative direction to operate the control valve. By the operation of the control valve, the fluid pressure of the fluid pressure source is controlled to a value corresponding to the travel of the input member. The working fluid pressure controlled by the control valve is produced as an output and the working unit is directly operated by the fluid pressure of this output. At the same time, the working fluid pressure also acts on the control valve in the inoperative direction. At this point, the control valve is operated according to the travel of the input member in such a manner that the force produced by the working fluid pressure balances with the force produced by the elastic member.
Accordingly, the position of the control valve is fixed regardless of the travel of the input member when the fluid pressure source is in the normal state. Then, the input side and the output side of the fluid pressure boosting device can be separately operated. Even when the input side and the output side are separated, the control valve is controlled according to the travel of the input member in such a manner that the force produced by the working fluid pressure balances with the force produced by the elastic member, thereby exhibiting the function as a stroke simulator.
In this manner, since the fluid pressure boosting device of the present invention can exhibit the function as a stroke simulator even when the input side and the output side of the fluid pressure boosting device are separately operated, the travel of the input member can be ensured and the input travel of the input member can be freely set without affecting the output side after the working unit.
Further, the working fluid pressure for operating the working unit is controlled by the working fluid pressure control means regardless of the working fluid pressure for operating the working unit or the input of the input member during the operation of the fluid pressure boosting device. Therefore, when the fluid pressure boosting device of the present invention is applied to a brake fluid pressure boosting device, the brake fluid pressure boosting device can easily and flexibly cope with such a system requiring to control the working fluid pressure regardless of the input of the input member during the operation of the fluid pressure boosting device. Therefore, for example, the working fluid pressure can be controlled or decreased for the regenerative braking operation by such a regenerative coordination brake system as mentioned above and the working fluid pressure can be controlled or increased for the brake assisting operation by a brake assist system also as mentioned above.
Further, when the input member is not operated, the working fluid pressure for operating the working unit can be controlled by the fluid pressure control means regardless of the operation of the input member, the fluid pressure boosting device can easily and flexibly cope with such a system requiring automatic brake controls, for example, a brake control for controlling the distance from another vehicle, a brake control for avoiding a collision with an obstacle object, and a brake control for Traction Control.
Since a control valve and a lever of a conventional fluid pressure boosting device can be used as the control valve and the lever of the present invention without significant change, the fluid pressure boosting device of the present invention can be manufactured with easy structure and at a low cost without using special parts.
Since the working unit can be operated by forward movement of the input member in case of the fluid pressure source failure, the working unit can be securely operated even in case of the fluid pressure source failure.
In the brake system of the present invention, when braking force larger than that for the normal braking (service braking) is required, for example, for brake assist control, brake control during running on a downward slope, or brake control during running with a full load capacity, or when braking force smaller than that for the normal braking (service braking) is required, for example, for regenerative brake coordination control, engine brake control, or exhaust brake control, one of the other controllers (control ECUs) for conducting the respective controls outputs a request signal requesting an increase or decrease in the braking force at the wheel cylinders. Then, the controller for the working fluid pressure control means controls the output of the brake fluid pressure boosting device according to the amount of increase or decrease in the braking force requested by one of the other controllers regardless of the input or pedal force on the brake pedal.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.